1. Field of the Invention
The present invention relates to cooling apparatus such as refrigerators, air conditioners, etc. utilizing a cold-accumulation material therein.
2. Description of the Prior Art
A cold-accumulation material is provided in a refrigerating device, such as a refrigerator and an air conditioner, in order to improve the efficiency of its refrigerating cycle. An example of such a refrigerating device is disclosed in Japanese Utility Model Publication No. 53-10586, filed on Oct. 9, 1973 in the name of Kenichi KAGAWA. In Japanese Utility Model Publication No. 53-10586, the refrigerating cycle has an auxiliary cooler and an auxiliary condenser placed within a case also containing a cold-accumulation material. The auxiliary cooler and the auxiliary condenser are connected in parallel with each other. When a load to be cooled is small, the auxiliary cooler cools the cold-accumulation material thereby accumulating an extra cooling capacity for later use. When the load to be cooled is large the auxiliary condenser supplements the condensing capacity of a main condenser by transferring heat between the cold-accumulation material and the main condenser. Thereby, the efficiency of the refrigerating cycle, especially the operating efficiency of the compressor, is improved.
Recently, there has been consideration of refrigerating cycles having cold-accumulation materials therein for the purpose of evening out power demand during a 24-hour day by better utilizing power which is not efficiently used, such as night-time power. As is shown in FIG. 1, a refrigerating cycle can be, for example, constituted as follows. A discharge side of a compressor 5 is connected through a condenser 7 and a first capillary tube 9 to an inflow side of a flowpath control electromagnetic valve 11. The valve 11 has two outflow ports. One outflow port connects through a second capillary tube 13 to an inflow port of a main evaporator 15. An outflow port of the main evaporator 15 connects through an accumulator 17 to an intake side of the compressor 5, whereby there is established a refrigerant flowpath for an ordinary cooling operation, which we shall also refer to as first mode cooling. During first mode cooling, refrigerant compressed by compressor 5 flows into the main evaporator 15 and evaporates therein to cool refrigerator compartments. The other outflow port connects through a third capillary tube 19 to an inflow-port of a cold-accumulation evaporator 21. An outflow port of the cold-accumulation evaporator 21 connects through the accumulator 17 to the intake side of the compressor 5, whereby there is established a refrigerant flowpath for a cold-accumulation operation which we shall also refer to as third mode operation. When the cold-accumulation material 23 is to be cooled (third mode), refrigerant compressed by compressor 5 flows into the cold-accumulation evaporator 21 and evaporates therein to cool the cold-accumulation material.
A thermosiphon 25 having a electromagnetic valve 27 therein is in thermal contact with both the main evaporator 15 and the cold-accumulation evaporator 21 and hence the cold-accumulation material 23. Cooling by means of the cold-accumulation material also referred to herein as second mode cooling is effected by heat transfer between the main evaporator 15 (and hence the refrigerator compartments) and the main evaporator 15 when the electromagnetic valve 27 is opened. Outflow ports of both the main evaporator 15 and the cold-accumulation evaporator 21 are connected to the accumulator 17. There may be different amounts of refrigerant evaporated in the respective evaporators during the ordinary cooling (first mode) carried out by main evaporator 15, and the cold-accumulation operation (third mode), carried out by the cold-accumulation evaporator 21.
During cold-accumulation operation (third mode) there may be a comparatively large amount of refrigerant flowing from the cold-accumulation evaporator 21. The cold-accumulation material 23 is thermally insulated from the surroundings. As the cold-accumulation operation continues, the amount of heat exchanged between the cold-accumulation evaporator 21 and the cold-accumulation material becomes smaller and hence the amount of refrigerant evaporated in the cold-accumulation evaporator 21 becomes smaller. The accumulator 17, therefore, may have to be designed so that the amount of refrigerant circulating in the refrigerating cycle has an appropriate valve in both ordinary cooling operation and cold-accumulation operation. If the accumulator capacity is too small, there is a risk of the phenomenon known as "liquid back-up" occurring. During liquid back-up, liquid refrigerant from the cold-accumulation evaporator 21 flows back into the compressor 5 during the cold-accumulation operation. This has an adverse effect on the reliability of the compressor 5 as well as lowering the efficiency of the refrigerating cycle. Simply increasing the size of the accumulator 17 involves the penalties of increased overall refrigerating device size and increased costs, as well as lowering the efficiency of the refrigerating cycle during the ordinary cooling operation. Therefore, the capacity of the accumulator is significant. The accumulator may have to be designed so that during both ordinary cooling operation and the cold-accumulation operation the amount of refrigerant circulating in the refrigerating cycle is appropriate. In general, such design, however, is very difficult. Therefore the accumulator capacity is usually designed to be larger than normally required to avoid any problem. Moreover, in the above-mentioned refrigerating cycle, liquid refrigerant flowing from the cold-accumulation evaporator 21 without having been completely evaporated therein may evaporate, to no useful effect, in the other parts, such as e.g., suction pipes, constituting the refrigerating cycle, thereby causing loss of efficiency.